Control system for electron discharge devices



April 3, 1935. w. D. COCKRELL 1,998,950

CONTROL SYSTEM FOR ELECTRON DISCHARGE DEVICES Filed Feb. 25, 1932 V Inventor: Wi'l Iiam Dcockrel I,

His Attobney.

Patented Apr. 23, 1935 CONTROL SYSTEM FOR. ELECTRON DISCHARGE DEVICES William D. Cockrell, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application February 25, 1932, Serial No. 595,028

3 Claims.

My invention relates to apparatus for measuring the length of moving objects and it has for its object the provision of improved apparatus for this purpose which is rapid and reliable in its operation and avoids the use of any mechanical part to contact with .the moving objects.

My invention will be better understood from the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the single figure of the drawing which is a diagrammatic representation of one embodiment of my invention, I have chosen to illustrate it as arranged to measure the length of each of a plurality of successive bars or plates, one of which is shown at I, which are passed along the rollers 2 in the direction indicated by the arrow. I project across'the path of the moving object a plurality of light beams represented by the dot and dash lines 3, 4, 5, and 6, which beams may be produced by any suitable means, such for example as by the separate lamps The spacing of beams 4, 5, and 6 from beam 3 will depend upon the lengths of the objects I to be measured, these spacings being represented by convenience by the letters a, b, and respectively. Arranged at'the opposite side of the path of travel from the lamps I are a plurality of photo-electric devices, such for example as photo-electric tubes, each positioned so that its window receives light from the light of one of the beams. The photo-electric device which receives beam 3 I shall term the master device and is represented by the letter M. The other photo-electric devices which receive beams 4, 5, and I shall term auxiliary devices and are represented by the letters Al, A2, and A3 respecively. Operatively connected with the auxiliary photo-electric devices Al, A2, and A3 are the indidcating or signaling devices Bl, B2, and B3 respectively. If the object to be measured has a length greater than a and less than b, the indicator BI will be operated. Likewise if the length of the article is greater than I) and less than c, indicator B2 will be operated, and lastly if the length of the article is greater than c, indicator B3 will be operated. The apparatus by which these results are brought about will now be described.

Connected between the sides 8 and 9 of a suitable source of direct current supply are the two voltage dividers l0 and II. The several photoelectric devices have their anodes connected with divider II by the adjustable connections l2 and have their cathodes connected with the negative side 8 of the supply through resistors 3. The cathodes of the photo-electric devices connect also with the grids of the electron discharge devices l 5,15, l1, and 8 respectively. The cathodes of the devices I5 to |8 inclusive are supplied from a common heating circuit I9 which is supplied by a transformer of which the secondary only is shown, and the midpoint of this secondary connects at 2| with the voltage divider ID. The anode of the discharge device l5 connects directly through the resistance 23 with the voltage divider ID at the point 24 which is positive with respect to the point of connection 2|. The anodes of the discharge devices l6, I1, and |8 also connect through the resistor 23 with voltage divlder l0, but each includes in addition a resistor 25, these resistors being many times larger than resistor 23. The anodes of discharge devices I6, i1, and I8 connect through the limit resistors 26 with the control grids 28, 29, and 30 respectively of the vapor electric discharge devices 3|, 32, and 33. The cathodes of the latter devices are connected to be supplied from a common heating circuit which is supplied with alternating current through a transformer of which the secondary 36 only is shown. The midpoint of this secondary connects through the sliding contacts 31 of the time delay switch 38 with the voltagedivider H1 at the point 39. The anodes of the vapor devices 3|, 32, and 33 connect with the positive side 9 of the source of supply through the windings of relays 42, 43, and 44 respectively. These relays control the circuits of the indicating devices Bl, B2, and B3. Relay 42 in addition to controlling the indicating device B| also controls the winding of the time delay relay 38 which relay is preferably so set that the time required for it to open up its controlled circuit is slightly more than the time required for one of the objects to be measured to travel from light beam 4 to light beam 6.

The operation of the apparatus is as follows. Before an'object to be measured reaches the first light beam 3, such position being illustrated in the drawing, the resistances of the several photoelectric devices are a minimum, since each receives the uninterrupted light from its respective lamp and the electron discharge devices I5 to I8 inclusive all are operative. Because of the combined IR drop through resistor 23 and each of the on the voltage divider and consequently to the cathodes of the vapor devices. Thus the vapor devices 3|, 32, and 33 are inoperative to pass current and indicators Bl, B2, and B3 remain dark. As the object I passes on and intercepts light beam 3 to the master photo-electric device M, electron discharge device l5 becomes inoperative. However, the anode potentials of devices I8, H, and i8 still remain negative with respect to the point 39. The vapor devices 3|, 32, and 33 therefore remain inoperative to pass current. As the object i passes on and intercepts beam l while still intercepting beam 3 the electron discharge device i6 becomes inoperative. As a result the anode potential of this device and hence the potential of grid 28 now becomes positive with respect to the point 39 since there is no longer any IR drop through resistance 25. Vapor device 3i immediately begins to pass cur rent energizing relay 42 which in turn causes indicator Bl to become energized and also energizes the winding of the time delay relay 38. If object I is of sufficient length, it may successively intercept beams 5 and 6 while still intercepting beam 3. Accordingly the electron discharge devices H and 58 will successively become inoperative and in the same manner as has been described above, and the vapor devices 32 and 3? will each in turn begin to pass current and through the relays 53 and i l cause the respective energization of the indicators B2 and B3. Thus if the observer sees all three indicators operative he knows that the article has a length which is as long or longer than the distance c.

If on the other hand the object 5 has a length which is greater than b and less than c it will be seen that after the interception of beam 5 and prior to the interception of beam 6, beam to the master device M will be restored. This restoration of beam 3 will cause the electron discharge device to again become operative. Because of the IR drop in resistor 23 due to the anode current of device it the anode potential of device it and hence of grid 39 is rendered negative with respect to the point 39 and will remain so even after the device i8 is rendered inoperative by the interception of light beam Thus the indicator B3 will fail to become 0perated and the observer will see only indicators Bi and 132. Hence he knows that the object l in this case has a length which is greater than b and less than 0. Likewise, if indicator Bi only is seen to operate the observer knows that the object has a length which is greater than a and less than 1). It is obvious that if none of the indicators BI, B2 or B3 operate the length of the object is less than a since in that case beam 3 is restored before beam l is intercepted, the restoration of beam 3 being effective to restore device iii to its original operative condition whereby indicators Bl, B2, and B3 cannot operate. As mentioned above, it will be understood that the time delay relay is so adjusted that it will open the cathode circuit of the vapor devices to render them inoperative to pass current only after sufiicient time has elapsed after the interception of beam 4 for the object to have passed somewhat beyond the point of interception of beam 6. After each interruption of the cathode circuit by switch 38 the switch quickly falls back to its original closed circuit position ready for the next energization.

I have chosen the particular embodiment described above as illustrative of my invention and it will be apparent that various other modifications may be made without departing from the spirit and scope of my invention which modifications I aim to cover by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

i. In combination, a source of current supply, a master electron discharge device and a plurality of other electron discharge devices each having a plate connected to be supplied from said source, means in the plate connection of each of said other devices for varying the plate voltage individually or" each device in response to the operation thereof, a voltage responsive device connected with the plate of each of said other devices and means responsive to the operation of said master device for varying the plate voltage of all of said other electron discharge devices.

2. In combination, a source of current supply,

a grid controlled master electron discharge device and a plurality of other grid controlled electron discharge devices each having a plate connected to be supplied from said source, means for separately controlling the grid of each of said devices, means in the plate connection of each of said other devices for changing the plate voltage in response to the operation of the device, a plurality of vapor electric discharge devices each having a grid connected with the plate of one of said other devices and an impedance common to the connection of all of said plates with said source whereby the operation of all of said vapor devices is controlled by the voltage drop in said impedance in response to the operation of said master device.

3. In combination, a source of current supply, a. grid controlled master electron discharge device having a plate, a plurality of other grid controlled electron discharge devices each having a plate, a connection between said source and all of said plates, a resistor therein common to all of said plates, a separate resistor in the connection to the plate of each of said other devices, a plurality of vapor electric devices each having a grid connected with the plate of one of said other devices whereby each of said vapor devices passes current in response to a minimum current in the plate of the discharge device by which it is controlled when the plate current of the master device is a minimum and all of said vapor devices are prevented from passing current when the plate current of the master device is a maximum.

WILLIAM D. COCKRELL. 

